Liquid amidoamine softeners have been described in the prior art. U.S. Pat. No. 5,154,838 (corresponding to EP 0459211A2) to Yamamura, et al. (assigned to Kao Corp.) discloses an aqueous liquid softener composition based on an amidoamine compound which is the condensation reaction product of a di- or tri-amine of formula (I) EQU R.sup.1 NH(C.sub.m H.sub.2m NH).sub.n H (I)
with a fatty acid of formula (II) ##STR1## wherein R.sup.1 represents a straight or branched chain, saturated or unsaturated hydrocarbon group having 8 to 24 carbon atoms, R.sup.2 represents a straight or branched, saturated or unsaturated hydrocarbon group having 7 to 23 carbon atoms, m represents 2 or 3, and n is 1 or 2. These compounds, which are neither hydroxylated or ethoxylated, are noted to have high dispersibility in rinse water, especially when the amidoamine compound is used in the form of its neutral salt.
In U.S. Pat. No. 5,133,885 to L. Contor, et al. (assigned to Colgate-Palmolive Co., the assignee of the present invention) fabric softening compositions are described which are aqueous dispersions of a fatty acid ester quat of formula ##STR2## where one or two R groups represent an aliphatic ester residue of from 12 to 30 carbon atoms of formula CH.sub.2n OCOR.sub.4, and the remaining R groups represent lower aliphatic, aralkyl or hydroxyalkyl groups, X.sup.- is an anion and "a" represents the ionic valence of the anion, and a fatty acid amidoamine softener of formula ##STR3## where R.sup.1 is a C.sub.12 to C.sub.30 alkyl or alkenyl group, R.sup.2 represents RT.sup.1,R.sup.1 CONH(CH.sub.2).sub.m or CH.sub.2 CH.sub.2 OH; R.sup.3 represents hydrogen, methyl, or (CH.sub.2 CH.sub.2 O).sub.p H, m is a number of 1 to 5 and p is a number of 1 to 5, at a weight ratio of ester quat to amidoamine of from 10:1 to 1:10.
The combination of organic acid with cationic fabric softener such as amines and quaternary ammonium compounds is extensively disclosed in the prior art. U.S. Pat. Nos. 3,904,359 and 3,954,630 to Ramachandran disclose a fabric treating composition comprising a complexing acid such as citric or maleic acid in combination with a quaternary ammonium compound or amines such as primary tallow and primary coco amine. The function of the acid, as stated in the patents, is to prevent yellowing of fabrics due to build-up of cationic softener and to provide a complexing site for metal ions contained in soils. U.S. Pat. Nos. 4,828,722 to Steltenkamp and U.S. 4,869,836 to Harmalker disclose multicarboxylic acid complexes of tertiary amines formed from a tertiary amine and a carboxylic acid selected from among citric acid and di and tri carboxylic acids having 21 to 54 carbon atoms. In U.S. Pat. No. 4,828,856 there is disclosed a fabric softener composition comprising a combination of carboxylic acid and amines having a long chain alkyl or alkenyl radical.
Although satisfactory results may be obtained with one or more of these prior art fabric softening compositions, further improvements are needed in terms of being able to provide efficacious fabric softening with a biodegradable cationic fabric softening compound, concomitant with the ability to substantially solubilize and remove mineral encrustation from the fabrics to be treated. This is a particularly important need for European fabric conditioning compositions where the cumulative deposition of mineral salts on fabrics during repetitive laundering in hard water is an acute problem. Moreover, the increased emphasis in Europe on using biodegradable softening compounds which have no toxic effect on aquatic organisms in aqueous effluent streams makes it imperative that conventional softening compounds, most notably, the di-long chain, di-short chain quaternary ammonium compounds be replaced as the softening compounds of choice in commercial rinse-cycle softening compositions with softening compounds which are significantly more compatible with environmental concerns.